Several hydroxyated metabolites or ethotoin were identified by gas-chromatography mass spectroscopy in urine of patients receiving ethotoin. These are: 2-phenylhydantoic acid; ortho, meta, and parahydroxy ethotoin; 3,4 dihydroxyphenylethotoin, 3 methoxy-4-hydroxyphenyl hydantoin; ethotoin dihydrodiol; 5-hydroxy-5-phenylhydantoin, 5-hydroxyethotoin and 5-hydroxy-5(4'-hydroxyphenyl)ethotoin.